2. Describing Motion
• Motion :- Motion is the change in position
of a body with time.
• Motion can be described in terms of the (i)
distance moved or the (ii)displacement
(i)Distance moved is the actual length of the
path travelled by a body.
(ii)Displacement is the length of the shortest
path travelled by a body from initial
position to it’s final position.
3. Example of the motion
The average speed
of bullet train is
320km/hrs
A car is in
motion.
Motion of the
Ball Downward.
4. • i) Uniform motion :- If a body
travels equal distances in equal
intervals of time, it is said to be in
uniform motion.
• ii) Non uniform motion :- If a
body travels unequal distances in
equal intervals of time, it is said to
be in non uniform motion.
Uniform motion and Non
uniform motion
5. Example
A movement of a asteroid
and the bouncing of ball
is the example of non
uniform motion.
The movement of
clock’s hand and
movement of
pendulum is the
example of uniform
motion
6. • Speed :- of a body is the distance travelled
by the body in unit time.
Speed = Distance/Time
• If a body travels a distance s in time t
then its speed v is v= s/t
• The SI unit of speed is meter per second
m/s or ms -1
. Since speed has only
magnitude it is a scalar quantity.
7. Example
The red car is at the speed of
30m/s
And,
The gray car is at the speed of
40m/s
9. Example Problems
Q. A car travels 85km from point A to B , then 45km
from point B to C . The total time took was 1.3 hrs.
What was the average speed of the Car?
Solution of the problem
Total distance=Distance covered i)A to B + ii)B to C
85km + 45km= 130km
Total Time = 1.3 hrs
Average speed = Total Distance Covered/Total time
=> 130/1.3 km/hrs
=> 100km/hrs
10. The quantity which specifies both
the direction of motion and speed
is velocity.
• Velocity of a body is the
displacement of the body per unit time.
Velocity =Displacement/time taken
• Since velocity has both magnitude and
direction, it is a vector quantity.
12. Average Velocity
• Average velocity :- is the ratio of the
total displacement to the total time taken.
• Average velocity =Total Displacement/Total
Time.
• Average velocity is also the mean of the
initial velocity u and final velocity v.
• Average velocity= (initial velocity + finial
velocity)/2
or
(u+v)/2
• Speed and velocity have the same units m/s
or ms -1
13. Example Problem
Q. If a car changes its speed from 10m/s to
20m/s in just 5 sec. What is the average
velocity of the car?
Sol. u = 10m/s time taken
v = 20m/s = 5sec
Average velocity = (u + v)/2
Þ (20m/s + 10m/s)/2
Þ 30m/s/2
Þ 15m/s
14. The quantity which specifies changes
in velocity is acceleration.
• Acceleration :- is the rate of
change of velocity.
• Acceleration = (Final velocity –
initial velocity) / 2
• If the velocity of a body changes
from initial value u to final value v
in time t, then acceleration a is
a = (v-u) /2
• The SI unit of acceleration is ms - 2
16. Distance –Time Graph
• Motion can be represented on the distance
time graph.
• In the graph distance is taken on the y –
axis and time is taken on the x – axis.
• The distance time graph for uniform
speed is a straight line.
• This is because in uniform speed a body
travels equal distances in equal intervals
of time.
18. Derivation of three formula of
motion
• Let a body is moving with initial velocity ‘u’ with
uniform acceleration ‘a’ it’s velocity become ‘v’
in time ‘t’ sec. In the meantime it covers the
distance ‘s’
• The term would be in
1. Acceleration -> m/s2
2. Initial and final velocity -> m/s
3. Time -> sec
4. Distance -> m
19. 1st
Equation of motion
• Acceleration = (v – u)/t
a = (v - u)/t
Þ at = v – u
Þ u + at = v
1st
equation
of motion
20. 2nd
Equation of motion
• Average velocity = (v + u)/2
• Distance Travelled = Av. Velocity + time
s = (v + u)/2 x t
Put v = u + at
Þ s = (u + at + u)/2 x t
Þ s = (2u+at)/2 x t
Þ s = (2ut + at2
) /2
Þs = ut + ½ at2
2nd
Equation of
motion
21. 3rd
Equation of motion
• We know that v = u + at
Þ v – u = at
Þ (v - u)/a = t
• Put t = (v – u)/a in eq. s = ut + ½ at2
s = u{(v – u)/a} + ½a {(v-u)/2} 2
Þ s = (uv - u2
)/a + ½a{(v2
+ u2
-2uv)/a2
}
Þ s = (uv - u2
)/a + ½(v2
+ u2
-2uv)/a
Þ s = (uv - u2
)/a + (v2
+ u2
-2uv)/2a
Þ s = (2uv - 2u2
+ v2
+ u2
-2uv)/2a
Þ s = (v2
- u2
)/2a
Þ 2as = v2
- u2
3rd
Equation
of motion
22. Circular motion
• The motion of a body in a circular path is called
circular motion.
• Uniform circular motion :- If a body moves
in a circular path with uniform speed, its motion is
called uniform circular motion.
• Uniform circular motion is accelerated motion
because in a circular motion a body continuously
changes its direction.
• The circumference of a circle of radius r is given by
2лr. If a body takes time t to go once around the
circular path, then the velocity v is given by
v = 2лr/2
